Copolyester-carbonates are a class of thermoplastics that, due to their many excellent properties, are utilized in many commercial and industrial applications as engineering thermoplastics. They are members of the tough thermoplastic family and exhibit excellent properties of toughness, flexibility, high heat distortion temperatures, and the like. These copolyester-carbonates may be prepared, as disclosed in U.S. Pat. No. 3,169,121, by the coreaction of a carbonate precursor, a dihydric phenol, and a difunctional carboxylic acid.
However, these copolyester-carbonates suffer from the disadvantage that they are somewhat flammable. Thus, copolyester-carbonates are sometimes unsuitable for certain applications where high temperature and/or exposure to flame may be encountered. In order to render the copolyester-carbonates suitable for high temperature and/or open flame environments they must first be modified to be rendered flame retardant. This modification involves either adding certain additives to the copolyester-carbonate resins or incorporating certain moieties, such as halogen containing moieties, into the copolyester-carbonate polymer itself. However, the presence of these flame retardant additives or halogen containing moieties may sometimes have a deleterious affect on the advantageous physical properties of the copolyester-carbonates, such as for example the impact strength.
It would thus be very advantageous if compositions comprised of halogen-free copolyester carbonate resins could be provided which exhibit flame retardant and non-dripping properties, which are economically competitive with non-flame retardant copolyester-carbonate compositions, and which simultaneously exhibit, to a substantial degree, most of the advantageous physical properties of unmodified copolyester-carbonate compositions such as good impact strength.
It is, therefore, an object of the instant invention to provide copolyester-carbonate resin compositions which are flame retardant, non-dripping, are economically competitive with non-flame retardant copolyester-carbonate compositions, and which simultaneously exhibit, to a substantial degree, substantially most of the advantageous physical properties of unmodified copolyester-carbonate resins.